For example, a fuel pump includes a disc-shaped impeller that has vane grooves arranged with respect to the rotative direction thereof. The vane grooves, which are adjacent to each other, are partitioned. The impeller rotates to pressurize fuel flowing through a pump passage defined along the vane grooves. It is required to enhance discharge pressure of a fuel pump for enhancing spray performance of fuel injected from an injection valve. Discharge pressure of a fuel pump can be enhanced by increasing electricity supplied to a motor portion of the fuel pump. However, energy consumption of the fuel pump may swell due to increasing electricity supply.
According to U.S. Pat. No. 6,113,363 (JP-A-2000-240582), inclining angle of a surface defining each vane groove is restricted in a pump portion of a fuel pump, so that the pump portion and the fuel pump are enhanced in efficiency.
According to U.S. Pat. No. 5,486,087 (JP-A-7-189975), a fuel pump includes a pump portion having an inlet and a pump passage (pressurizing passage) that define a flow passage therebetween. The cross section of the flow passage is gradually reduced from the inlet toward the pump passage so as to enhance efficiency of the pump portion. Discharge pressure of the fuel pump can be increased by enhancing the pump efficiency, while energy consumption of a motor portion is restricted.
In recent years, it is required to further enhance the pump efficiency corresponding to demand for increasing in fuel discharge pressure and/or discharge amount of fuel.